G protein-coupled receptors sense an astonishing variety of extracellular molecular signals and trigger complex intracellular and physiological responses. They share a common architecture of seven transmembrane helices connected by a broad range of intra- and extra-cellular loops and terminal domains. Structure determination feasibility of this protein family was demonstrated recently with the first high resolution studies on the human Beta2 adrenergic, turkey Beta1 adrenergic, and human adenosine A2A receptors. The Center for Membrane Protein Structure Determination (CMPD) has been created to use a protein family specific platform to determine the high resolution structures of 15-20 representative GPCRs distributed across the phylogenetic tree. Receptor structures are needed at a biologically relevant granularity, for small molecule ligand receptors, peptide and protein receptors, lipid receptors, class B-F receptors, and of receptors in the active and inactive functional states. Each receptor structure will be determined with a set of different pharmacological ligands to define the receptor binding site(s). Solution studies will be conducted with purified receptors bound to different ligands to understand receptor dynamics using hydrogen-deuterium exchange and NMR spectroscopy. In collaboration with the NIH screening center, a library of small molecule probes will be used to analyze each receptor and discover allosteric binding sites using a high throughput thermal stability screen. Through a biologically informed selection of representative receptors, we will maximize the CMPD's impact through computational modeling of close homolog's and functional studies by external collaborators thereby establishing The PSI GPCR Network. The generated data will be provided to the community in a time frame consistent with the guidelines of the Protein Structure Initiative. Technology access will be achieved through on-site training, workshops, meetings, and publications. Processing access to the CMPD core facility will be provided through a 30% pipeline capacity commitment for the PSI: Biology Network nominated targets. Based on the experience of the CMPD investigators, preference will be for human or eukaryotic membrane proteins to maximally leverage the CMPD capabilities.